Wafer tubes typically comprise an image input window bonded to a photocathode, an MCP, to provide electron amplification, and, an imaging phosphor screen. These components are mounted in a vacuum envelope and electrically biased. The MCP is formed with input and output electrodes, which are conductive coatings on the input and output surfaces of the MCP. Traditionally, standard type MCPs do not receive further processing after deposition of electrodes on the input and output surfaces. Typically the electrodes are nichrome or inconel coatings in the case of standard units, and for feedback limited MCPs (FLMCPs) a thick coating of, for example, aluminum, is deposited on the output end of the MCP as more fully described in copending application Ser. No. 07/724,041 entitled Feedback Limited Microchannel Plate Apparatus and Method and filed in the names of Aebi and Costello, now U.S. Pat. No. 5,268,612 which issued on Dec. 7, 1993.
In general, in the manufacture of standard type night vision tubes, almost all meet specifications and do not include defects due to emission points on the output end of the MCP which disrupt and distort the output image. This type of distortion will be found only in about 4% of the typical manufacturing run. However, this problem is significant in the manufacture of enhanced tubes. Here losses as high as 50%, depending on the specification for the tubes being fabricated, may be typical. An enhanced tube, for example, may comprise a wafer tube in which the positioning of the MCP is closer to the output phosphor than would be the case for a standard tube or a FLMCP.